The results of two community surveys of the koala population in the Gunnedah region in New South Wales taken in 1990 and 2006 were compared. The survey of 1990 was initiated after the charismatic marsupial became a mascot for a tree planting program to address the problem of salinity on agricultural land in the area. As koalas were later reported to be using these planted trees, another survey was conducted in 2006 at a broader geographical scale. Although the surveys employed different methodologies, these two datasets allowed some broad conclusions to be made about changes in the region’s koala population over time.

Koalas were reported to occupy a broader extent in 2006 than in 1990, spreading to the region’s north and east and into developed and agricultural areas. In 1990, koalas were found most frequently in environments surrounded by at least 40% wooded vegetation, whereas this decreased to 25% in 2006. Similarly, the core of the reported range shifted from the basalt hills in the southern end of the region in 1990 to the town centre in 2006. In both surveys, no koala sightings were reported in the vegetated hilly margins of the region. Contrary to state-wide trends, the results of these surveys seem to indicate that the koala population in the Gunnedah region is expanding.

The apparent growth in koala sightings in the Gunnedah region in part reflects the changing distribution of the population but is also a result of sampling bias. For instance, a landowner’s increased willingness over time to report a koala sighting on their property may falsely imply the population’s increasing extent. Conversely, an absence of koala sightings from remote or wilderness areas may simply occur because observers rarely travel through these areas. Thus, the shifting centre of the surveyed koala population from the basalt hills to the town centre may represent actual movement of koalas into the area or, alternatively, an improved survey effort in the town. It is known, however, that koalas have increasingly made use of areas revegetated in the 1990s.

Research efforts have increased in recent years to address the declining koala population in New South Wales. In the Gunnedah and surrounding regions, in particular, the topics of leaf and soil chemistry, diseases, tree choice and movement patterns by koalas are of utmost interest for understanding population dynamics in the area. The authors of this study argue for a sustained and systematic assessment of the region’s koala population in addition to studies of the factors that may alter it over time.

Summarised by Joanna Horsfall

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